Alternator Pulley

[Muzzie]

I've had my alternator upgraded, but it seems to be struggling alot - to the point where at night the lights flash with the stereo and the voltage gauge hovers around 12 volts.

Thats at about 2000 rpm, but if I shift down and bring the revs up to about 3500 everything goes right and voltage gauge goes up to just under 13 volts. So I'm wondering if it's just the pulley is too big?

Would this be the case? Or another reason. And is it as simple as bolting a smaller pulley on?

[Corona]

First thing that I would be checking is the Earths and the Power leads from the Alternator, then next could be as you suget, except I would put a smaller pully on the alternator as a larger one would make it go slower.
I do not know how long the Alt would last running at higher speeds tho.